This research will be done primarily in Uruguay at the Physical Biochemistry Laboratory, School of Science as well as the Biochemistry Department, School of Medicine at the University of the Republic, Montevideo, in collaboration with Dr. Denicola as an extension of NIH grant 1 R01 HL074391-02; 7/10/03 - 6/30/07. The experimental goals described in this FIRCA application address fundamental mechanisms underlying the principal source of morbidity and mortality in westernized countries, atherosclerosis. Specifically, the questions arose in the parent grant, how hydrophobic phases influence the kinetics and mechanism of NO reaction with O2, will be extended considering a clinically relevant hydrophobic environment:: the low density lipoprotein (LDL). It is hypothesized that the hydrophobic compartment of circulating LDL serves to catalyze and focus the reaction of NO with O2, yielding secondary nitroso (RNO) and nitrated (RNO2) products that translate the cell signaling actions of NO. Specifically, a mechanistic rationale is proposed for examining a relative shift in nitrosation vs. nitration under biological conditions. To address this concept, two key experimental aims will be pursued: 1) delineate the kinetics, mechanisms and novel product formation (nitrosation and nitration) from NO/O2 reaction within the LDL particle, and 2) identify the vascular signaling actions.(vasodilation and vascular anti-inflammatory action) of the NO/O2-modified LDL. The proposed investigations will provide a strong foundation for understanding the mechanistic basis of the effects of NO and O2 reaction on LDL oxidation and consequent atherogenic events in particular, and on vascular inflammation in general.